Demand delivery watering systems for pigs and sheep using animal actuated valves, as for example, Atchley, U.S. Pat. No. 3,734,063 granted May 22, 1973, are now used extensively. Many farms using such systems are located in geographic areas where temperature extremes occur. Clay Equipment Corporation of Seattle Falls, Iowa offered a circulating water system which attempted to prevent freezing by burying the distribution pipes below frost line so that the earth would warm the water in the winter and cool it in the summer. Applicant does not believe the system is still offered since it is believed that the system could not prevent freezing of the water bowls.
In 1977, Atco Manufacturing Co., Inc. designed a recirculating system for the Battelle Research Institute which was installed in the State of Washington in 1977. This system used nipple valves as set forth in U.S. Pat. No. 3,734,063, supra and the supply pipes were buried below the frost line. The system as furnished to Battelle was not placed in production because it had several serious design problems. First, if a power failure occurred, the electric heater ceased to function, the recirculation pump stopped and the water in the system froze under extreme cold conditions. Because the pipes were buried deep in the ground, the system could not be reactivated for weeks or even months. Further, the Battelle system failed when the amount of flow through the heating element was insufficient and the water was turned to steam thereby introducing air into the system and preventing the pump from circulating the water. The Battelle system also lacked a device for expelling air under any condition and did not have sensing devices to shut down the system when the water temperature in the system exceeded high levels.
Others have attempted to prevent the supply pipes from freezing by wrapping them with insulated electrical heating tape. Such systems work satisfactorily until the electrical power system fails. A standby diesel-electric system is generally too costly.
Since power system failure is frequent in many regions with cold climates, no automatic recirculating system is sufficiently reliable unless there is automatic freeze protection in the event of power failure.